I have a 2001 SB formula 155 with a 65 curtis fin. It behaves perfect going upwind but downwind the board starts to make weird things when the sail gets powered(diablo 8.2 with about 7-10 knot wind). I feel the tail of the board like loosing contact or adherence to water and the sail trying to propel me forward. I am a 180 lb. beginner-intermediate
Could be the fin too long? I tried the same fin on a Go 200 and does the same.

Sometimes a too-big fin will cause spinout if you're overpowered and planing fast downwind, but that's definitely not something I would expect you to experience in 7-10 knots with an 8.2.

If this is happening when you're not planing and not in the footstraps then it's probably just a beginner thing. I.e. the fin is starting to provide lift and asking that you get back toward the footstraps and break the board free onto a plane.

It happens when I am about to plane and trying to put my feet at the back. The tail starts to wave. The wind was not enough for planing 90% of the time
Is spin out caused by too much lift?
What is tow?
You can see I am a beginner

It happens when I am about to plane and trying to put my feet at the back. The tail starts to wave. The wind was not enough for planing 90% of the time
Is spin out caused by too much lift?
What is tow?
You can see I am a beginner

The fin is fine. It is right for the board, I belive, but probably bigger than ideal for that sail. There is a lot of real-estate on that board - foot position and balance as you transition to planing is really critical, in low wind you should practice trying to get into a balanced stance and plane out of the straps (you might get tossed) - I find it helpful to ignore the footstraps in marginal winds.

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